A cellular communications network typically includes a variety of communication nodes coupled by wireless or wired connections and accessed through different types of communications channels. Each of the communication nodes includes a protocol stack that processes the data transmitted and received over the communications channels. Depending on the type of communications system, the operation and configuration of the various communication nodes can differ and are often referred to by different names. Such communications systems include, for example, a Code Division Multiple Access 2000 (CDMA2000) system and a Universal Mobile Telecommunications System (UMTS).
Third generation wireless communication protocol standards (e.g., 3GPP-UMTS, 3GPP2-CDMA2000, etc.) may employ a dedicated traffic channel in the uplink (e.g., a communication flow between a mobile station (MS) or User Equipment (UE), hereinafter referred to as a user, and a base station (BS) or Node B. The dedicated physical channel may include a data part (e.g., a dedicated physical data channel (DPDCH) in accordance with UMTS Release 4/5 protocols, a fundamental channel or supplemental channel in accordance with CDMA2000 protocols, etc.) and a control part (e.g., a dedicated physical control channel (DPCCH) in accordance with UMTS Release 4/5 protocols, a pilot/power control sub-channel in accordance with CDMA2000 protocols, etc.).
Newer versions of these standards, for example, Release 6 of UMTS provide for high data rate uplink channels referred to as enhanced dedicated physical channels. These enhanced dedicated physical channels may include an enhanced data part (e.g., an enhanced dedicated physical data channel (E-DPDCH) in accordance with UMTS protocols) and an enhanced control part (e.g., an enhanced dedicated physical control channel (E-DPCCH)) in accordance with UMTS protocols.
FIG. 1 illustrates a conventional wireless communication system 100 operating in accordance with UMTS protocols. Referring to FIG. 1, the wireless communication system 100 may include a number of Node Bs such as Node Bs 120, 122 and 124, each serving the communication needs of a first type of user 110 and a second type of user 105 in their respective coverage area. The first type of user 110 may be a higher data rate user such as a UMTS Release 6 user, referred to hereinafter as an enhanced user. The second type of user may be a lower data rate user such as a UMTS Release 4/5 user, referred to hereinafter as a legacy user. The Node Bs are connected to an RNC (radio network controller) such as RNCs 130 and 132, and the RNCs are connected to a MSC/SGSN 140. The RNC handles certain call and data handling functions, such as, autonomously managing handovers without involving MSCs (mobile station controller) and SGSNs (Serving GPRS Support Node). The MSC/SGSN 140 handles routing calls and/or data to other elements (e.g., RNCs 130/132 and Node Bs 120/122/124) in the network or to an external network. Further illustrated in FIG. 1 are interfaces Uu, Iub, Iur and Iub between these elements.
An example of a frame structure for the UMTS uplink dedicated physical channels is illustrated in FIG. 2A. Each frame 200 may have a length of, for example, 10 milliseconds (ms) and may be partitioned into 15 slots 205. Each slot 205 may have a length of, for example, 2560 chips, which corresponds to one power-control period, and may have a duration of, for example, 2/3 ms.
The uplink dedicated physical channels include a DPDCH 240 and a DPCCH 220, and each of the DPCCH 220 and the DPDCH 240 may be code multiplexed. The DPDCH 240 may include information transmitted from the legacy user 105. The DPCCH 220 may include control information, for example, a pilot signal 221, transmit power control information (e.g., transmit power control (TPC) bits) 222, a transport format combination indicator (TFCI) value 223 and feedback information (FBI) 224 (which may be used or unused).
The TFCI 223 may inform the Node B 120/122/124 of the transport format information (e.g., voice and/or data packets sizes, coding types, etc.) transmitted from the legacy user 105. The legacy user 105 and the Node Bs 120/122/124 may generate transmit power control (TPC) commands 222 to control each others transmit power. When a user 105 communicates with, for example, a single Node B 120/122/124, a single transmit power control command may be received in the TPC information 222 of each timeslot.
While FIG. 2A illustrates a 3GPP-UMTS uplink frame structure, a 3GPP2-CDMA2000 uplink frame structure may be similar. However, a typical 3GPP2-CDMA2000 uplink frame structure does not include the above-described TFCI 223 and FBI 224.
An example of a frame structure for the enhanced uplink dedicated physical channels (e.g., E-DPCCH and E-DPDCH), is illustrated in FIG. 2B. Each frame 200a may have a length of, for example, 10 milliseconds (ms) and may be partitioned into 15 slots 205a. Each slot 205a may have a length of, for example, 2560 chips, which corresponds to one power-control period, and may have a duration of, for example, 2/3 ms.
The enhanced uplink dedicated physical channels include an E-DPDCH 240a and an E-DPCCH 220a, and each of the E-DPCCH 220a and the E-DPDCH 240a may be code multiplexed.
The E-DPDCH 240a may include information transmitted from the user 110. The E-DPCCH 220a may include control information, for example, a happy bit (H-bit) signal, transport format combination indicator (E-TFCI), and retransmission sequence number (RSN), which are coded and occupy at least three slots (e.g., 1 subframe) within the frame of FIG. 2B.
The E-TFCI may inform the Node B 120/122/124 of the transport format of information (e.g., data packets sizes, TTI length, etc.) transmitted from the enhanced user 110.
FIG. 3A illustrates a conventional UMTS uplink transmitter 300 (e.g., located at the legacy UEs 105 of FIG. 1) and receiver 350 (e.g., located at one of Node Bs 120/122/124 of FIG. 1). Although FIG. 3A illustrates a conventional transmitter 300 and receiver 350 for transmitting uplink dedicated channels (e.g., DPDCHs and DPCCH) it will be understood that enhanced uplink dedicated channels (e.g., E-DPDCHs and E-DPCCH) may be transmitted and received in the same manner.
As shown in FIG. 3A, the transmitter 300 includes, for each of the DPDCH 240 and the DPCCH 220, a binary phase shift keying (BPSK) modulator 305, an orthogonal spreading unit 310, and a gain unit 315. Frames (e.g., frame 200) associated with the DPCCH 240 and the DPDCH 220 are modulated at respective BPSK Modulators 305, and the modulated frames are then orthogonally spread at the respective orthogonal spreading unit 310. The spread modulated frames are received by the gain units 315 where an amplitude of the spread modulated frames may be adjusted. The outputs of each of the gain units 315 are combined (e.g., code-division multiplexed) into a combined signal by a combiner unit 320. The combined signal is scrambled and filtered by a shaping filter 325, and the output of the shaping filter 325 is sent to the receiver 350 via a propagation channel (e.g., over the air).
The receiver 350 includes a matched filter unit 355 for filtering signals received from the transmitter 300, for example, on propagation path 330. That is, namely, the matched filter 355 performs a filtering operation in conjunction with that of the shaping filter 325. The filtered signal is sent to the processing block 360 and the multi-path acquisition unit 365.
The multi-path acquisition unit 365 analyzes a range of path positions or path offsets, alternatively referred to as “hypotheses”, and reports on positions within the range of path positions having a high signal energy (e.g., above a given threshold) as being “available”. The path management unit 370 compares the available paths with existing path information including path offsets received from the processing block 360. Based on the comparison, the path management unit 370 removes duplicate paths from the available paths and sends the resulting path information to the processing block 360 in the form of available paths information at a given interval. Likewise, the existing path information may be received by the path management unit 370 from the processing block 360 at the given interval. In an example, the given interval may correlate to each frame (e.g., every 10 ms).
FIGS. 3B and 3C illustrate process flows for conventional multi-path acquisition, which generally describe the processing in multi-path acquisition unit 365 of FIG. 3A. Referring to FIG. 3B, the pilot energy over a frame is calculated for a specific path position (hypothesis). The specific path position may be a path offset from the range of possible path offsets provided by the RNC or derived from the processing block 360 in the existing paths information as discussed in detail below.
Returning to FIG. 3B, the output from the matched filter 355 corresponding to this hypothesis (which is a complex signal) is descrambled and despreaded (310a), and the pilot pattern is also removed by function 310a as well. The output symbols corresponding to pilot bits are next accumulated (320a) by simple addition over each slot. The output of this block is at a slot rate, i.e., one (complex) output per slot.
Next, the L2-norm of the output from 320a is formed (330a). Assuming for example that the complex output signal is z=a+j*b, the L2-norm may be given by L2(z)=a2+b2. The L2-norms of the accumulated pilot signal are further accumulated over the frame interval (340a), and the resultant output is the frame pilot energy (350a).
Referring to FIG. 3C, the frame pilot energy for each hypothesis (355b) is compared with a threshold (365b). Hypotheses with frame pilot energy surpassing the threshold (output of 365 is ‘YES’) are reported (375b) to the existing and new paths management block 370 in FIG. 3A for further processing.
Returning to FIG. 3A, as stated above, the output from the matched filter 355 is also sent to the processing block 360 to generate DPDCH soft symbols for decoding the received signal with turbo decoders or convolutional decoders (not shown) to obtain the transmitted data. The processing block 360 may generate the existing paths information including path offsets, channel estimates, and mobility of the user 105 for received propagation paths based on the received signal, and provides this existing paths information to the existing and new paths management unit 370.
In one example, the mobility of the user 105 may be determined with a mobility indicator, which may be an estimate of the bandwidth of the propagation channel, alternatively referred to as a Doppler spread of the propagation channel. Methodologies for determining the mobility indicator are well-known in the art. In another example, the received signal frame energy for the received signal on the propagation paths may be the DPCCH energy over a given frame (e.g., frame 200).
The processing block 360 may use the available paths information from the existing and new paths management unit 370 in further processing the received signal. As discussed above, this available paths information may be acquired with processing previously performed at the multi-path acquisition unit 365 and a path management unit 370.
When the above conventional methods of multi-path acquisition are applied in a multi-user environment (e.g., including enhanced and legacy users), the presence of the enhanced users (e.g., Release 6 users) presents increased interference (e.g., interference to legacy users), which overshadows the power levels of legacy (e.g., non-Release 6) users. Thus, multi-path acquisition performance for legacy users may be degraded.